Noncentrosymmetric structural transitions in ultrashort ferroelectric AGaO$_{3}$/A'GaO$_{3}$ superlattices

TL;DR

This study uses density functional theory to explore how octahedral tilting influences noncentrosymmetric structural transitions and polarization in ultrashort AGaO$_{3}$/A'GaO$_{3}$ superlattices with various cation orderings.

Contribution

It reveals the specific octahedral tilt modes driving displacive transitions and demonstrates the hybrid improper ferroelectric mechanism inducing polarization in these superlattices.

Findings

Displacive transitions driven by two specific octahedral tilt modes.

Ground states of certain superlattices are polar.

Polarization arises from coupling of tilt modes via hybrid improper ferroelectricity.

Abstract

The effect of octahedral tilting on the acentric structural transitions in AGaO$_{3}$/A'GaO$_{3}$ [001], [110], and [111] superlattices (A, A' = La, Pr, Nd) is studied using density functional theory. We find the displacive transitions are driven by two octahedral rotations modes (a$^{-}$a$^{-}$c$^{0}$ and a$^{0}$a$^{0}$c$^{+}$ tilting), with amplitudes that depend on the A and A' chemistry and cation ordering direction. We find the ground states structures of the [001] and [111] ordered superlattices are polar. The coupling of octahedral tilting modes through a hybrid improper ferroelectric mechanism induces the polar displacements and produces the macroscopic electric polarizations.